The transmission of digital services, and more particularly of audio-visual services, over an IP network is the subject of standardization work within the DVB (“Digital Video Broadcasting”) group. The result of this work can be found in the document “ETSI TS 102 034 v1.1.1 (2004-06) Digital Video Broadcasting (DVB); Transport of MPEG-2 Based DVB Services over IP Based Networks”. This document should be considered, in the current phase, in the context of a client, called HNED (“Home Network End Device”) in the standard, directly connected to the service delivery network via a transparent gateway as shown in FIG. 1. In this diagram, the client therefore belongs to the delivery network and shares its IP addressing space and the domain name, among other things.
Among other things, this standard describes the discovery of services in such a network. It defines the mechanisms used to discover the services, select a service and issue service discovery information.
The first problem addressed is the mechanism used to identify the service providers and the services. A service provider is identified uniquely by the domain name under which he is registered and which he controls.
The various steps in the discovery process are as follows. Firstly, the service information entry points must be determined. Such an entry point corresponds to an IP address of a server providing access to information describing services offered. This description information is described in the form of XML files describing the list of services and, for each service, giving certain information including the address to which this service is transmitted.
The first problem solved by the standard is therefore the way in which the service discovery entry point or points are found. The standard defines a process for finding this or these entry points consisting in 5 different methods offered to the client. The client has to try these 5 methods in turn and stop at the first one giving it at least one valid entry point to the service discovery.
This standard should be considered in the context in which the client is connected transparently to the transmission network. The client is a member of this network. This requirement is strict, because it is commonplace to have a digital service client in fact connected to a local area network which can be a home network or an enterprise network. Normally, in this case, the local area network is connected externally to an external network, such as the service delivery network, via a non-transparent gateway. The local area network has its own addressing space different from the transmission network, known address translation mechanisms being implemented on this gateway.